1. Field of the Invention
The present invention relates to a method for manufacturing a wiring substrate.
2. Description of Related Art
In providing a multi-layer wiring substrate for connecting such chips such as IC and LSI chips, there has conventionally been used an organic wiring substrate having a construction including a dielectric layer comprised of a polymer material and an alternately laminated conductor layer. In recent years, the mainstream approach involves so-called “built-up” wiring substrates, in which the dielectric layers and conductor layers are laminated successively, one by one, while the electric connection between these layers is provided through a via hole drilled or bored by a laser processing method or photo-processing method.
Characteristically, in the manufacturing method for built-up wiring substrates, the via formation step uses laser processing and the conductor layer formation step employs pattern plating. In the conductor layer formation step, after the plating resist is patterned using photolithography technology, an electrolytic plating process is executed. When the plating resist is patterned, providing relative positioning accuracy between an exposure mask and a wiring substrate workpiece is an important key to producing accelerated, high precision wiring. Conventionally, the relative positioning between the exposure mask and the wiring substrate workpiece has been carried out based on the result of a picture taken of a positioning mark formed on the conductor layer with transmitted light. See, e.g., Japanese Patent Application Laid-Open No. 2001-217546.
In another approach, to improve the accuracy of relative positioning between the exposure mask and wiring substrate workpiece, an attempt has been made to provide photographing of the positioning mark using reflected light. According to the photographing method using transmitted light, a positioning mark formed on the conductor layer, which is the lower layer of the laminated layers, is photographed beneath resin dielectric layer in which filler is mixed.
According to the photographing method using reflected light, the positioning mark is formed by excavating the resin dielectric layer to expose the conductor layer and the mark is read using reflected light. Because filler such as silica is usually mixed in the resin dielectric layer, it is difficult to increase the transmission ratio of the light. Therefore, the reflection method can be expected to provide improved detection accuracy in detecting the positioning mark as compared with the transmission method. Further, improvement in the positioning accuracy of the exposure mask with respect to the wiring substrate workpiece can also be expected. However, because the positioning mark used in the reflection method is formed by excavating the resin dielectric layer using laser processing at the same time that the via conductor for the interlayer connection is formed, the process for producing the positioning mark itself has a processing accuracy determined by the laser processing operation. In order to improve exposure accuracy in reading the positioning mark using the reflection method, it is important to improve the accuracy of formation of the positioning mark.